1. Field of the Invention
The present invention relates generally to an adjustable-grip latch for releasably securing closures of industrial cabinets and the like. More particularly, the present invention relates to an adjustable-grip latch having a slippable, friction-type drive connection formed between an operating shaft and a pawl.
2. Prior Art
Adjustable-grip latches of a variety of configurations have been proposed for releasably securing industrial cabinet closures and the like. Such latches are particularly useful where it is desired (1) to compress a gasket which engages perimetrically-extending portions of a closure when the closure has been closed, or (2) to suppress vibration of a closure by clamping it snugly into engagement with such framework as defines the opening that is closed by the closure, or (3) to provide a tightly closing latch which will compensate for irregularities in manufacturing tolerances or for changes in dimensions due to wear.
One type of adjustable-grip latch which has been proposed includes a mounting ferrule, a shaft, a knob, a stop, a pawl, and a compression coil spring. A central portion of the shaft extends through and is journaled by the mounting ferrule. A forward end portion of the shaft carries the knob. A rearward end portion of the shaft is threaded into a threaded hole formed in the pawl. The stop extends alongside the rearward end portions of the shaft to limit the range of travel through which the pawl can move in response to rotation of the shaft. The compression coil spring is carried on the shaft, with one end of the spring engaging the pawl, and the other end engaging the mounting ferrule. The pawl and the stop are configured such that only a one-fourth turn of the shaft is needed to move the pawl between its latched and unlatched positions. The compression coil spring provides a slippable, friction-type drive connection for transmitting only a limited amount of torque from the shaft to the pawl, thereby enabling the shaft to move the pawl between its latched and unlatched positions, and enabling the shaft to rotate relative to the pawl when the pawl has engaged the stop.
The use of a compression coil spring to establish a slippable, drive connection between a pawl and a shaft in an adjustable-grip lock has a number of drawbacks. As the shaft is rotated relative to the pawl to move the pawl axially along the shaft, the degree to which the spring is compressed changes as the position of the pawl along the shaft is changed. One of the results of the change in spring compression is that the force required to turn the shaft increases with an increase in compression of the spring, and decreases as spring compression is relieved. Another result is that the torque which is transmitted from the shaft to the pawl during rotation of the shaft also varies. If the lengthy coil of wire which forms the spring should break at any point along its length, or if the open and exposed coils of the spring should become distorted, it is possible for the driving connection between the pawl and the shaft to fail, whereby neither latching or unlatching operations can be effected by rotating the shaft. Inasmuch as compression coil springs are relatively large in size, adjustable-grip latches which utilize compression coil springs are often found to require undesirably large mounting spaces.